Please refer to the following docs.
Application Tier Platform Migration with Oracle E-Business Suite Release 12 (Doc ID 438086.1)
Oracle E-Business Suite Upgrades and Platform Migration (Doc ID 1377213.1)
Export/Import Process for Oracle E-Business Suite Release 12 using 10gR2 (Doc ID 454616.1)
Export/import process for 12.0 or 12.1 using 11gR1 or 11gR2 (Doc ID 741818.1)
I've one stupid question, I'm planing to upgrade EBS 12.1.1 to 12.1.3, first should be upgrade or migrate??
It doesn't matter, you can either upgrade then migrate or migrate then upgrade.